Galvanic anode



July 21, 1959 H.A. ROBINSON 2,895,893

GALVANIC ANODE Originl Filed May 19. 1954 INVENTOR Hora/0'4 RobinsonATTORNEYS.

Patented July 21, 1959 GALVANIC AN ODE Harold A. Robinson, Midland,Mich, assignor to The Dow Chemical Company, Midland, Mich., acorporation of Delaware Original application May 19, 1954, Serial No.430,921. Divided and this application October 18, 1956, Serial No.616,888

3 Claims. (Cl. 204-197) This invention relates to metal cored galvanicanodes and to a method of making the same.

Galvanic anodes comprising a consumable portion, usually magnesium,which is cast around a steel core member have found considerable use inproviding cathodic protection to a wide Variety of materials which aresubject to electrolytic corrosion. Typical of the items receiving suchcathodic protection are pipe lines, tanker compartments, ship hulls,water heaters, and steam condensers.

In the past, some galvanic anodes have been made in batchwise manner bya permanent mold casting process. In this process, the steel or othermetal core is placed in a casting mold and the molten galvanic metalthen is poured around it and allowed to solidify. While anodes made upin this manner are satisfactory for many applications, they are ingeneral subject to some limitations which somewhat reduce their utility.

First, the bond between the core and the consumable portion of the anodetends to be a mechanical bond rather than a metallurgical bond. In mostcases, where the anode is several inches in length, a suflicientmetallurgical bonding occurs to provide good electrical contact betweenthe core and the consumable portion of the anode. However, in somecases, the mechanical bond is so slight that the core may be readilyremoved from the anode after casting.

Another difliculty with permanent mold casting of cored anodes is thatthe positioning of the core within the anode is difficult to control.This lack of uniformity in core placement results in difliculties inmounting the anode in certain applications where the anodes are to beattached to mounting means which are not capable of adjustment.Representative of such uses for galvanic anodes is the protection ofship hulls, in which a hollowcored anode is fitted over mounting studssecured to the hull. If the core is warped, the anode willnot easily fitover the threaded studs. A description of this type of anode may befound in the January 1953, issue of Motorship magazine.

A principal object of this invention is to provide improved metal coredgalvanic anodes having more uniform construction characteristics.

Another object of this invention is to provide an improved, moreeconomical metal cored galvanic anode.

Yet another object of this invention is to provide an improved method ofmaking galvanic anodes.

An additional object of this invention is to provide an improved methodof continuously casting metal cored galvanic anodes.

A further object of this invention is to provide a metal cored galvanicanode having improved metallurgical bonding between the core and theconsumable portion of the anode.

In accordance with the method of the present invention, galvanic anodesare made by a continuous process in which the consumable metal part ofthe anode is direct chill cast around an electrically conductive coremember which is fed through the bottomless chill-casting mold at thesame linear rate as that at which the casting is produced. Anodes of anyreasonable length may be made in this manner, with assurance that theposition of the core member within the anode may be controlled withinclose limits.

For the sake of brevity in the specification, the continuous process bywhich the consumable metal of the anode is direct chill cast is referredto as direct chill casting." Direct chill casting of ingots or billetsis a well established process. See, for example, U.S. Patents 2,135,183(Iunghans), 2,301,027 (Ennor), 2,410,837 (Peters), 2,503,819, (Gunn eta1.) and 2,548,196 (Barstow et al.).

The invention, as well as additional objects and advantages thereof,will best be understood when the following detailed description is readin connection with the accompanying drawings, in which:

Fig. l is a side elevational view, partly broken away and in section,showing direct chill casting apparatus suit able for use with thisinvention;

Fig. 2 is a fragmentary View, partly broken away and in section, ofsimilar direct chill casting apparatus, showing an alternative means offeeding molten metal into the mold;

Fig. 3 is a fragmentary view, partly broken away and in section, ofanother alternative form direct chill-casting apparatus in which themolten metal is applied along the core and above the level of moltenmetal in the mold;

Fig. 4 is a side elevational view, of a ships hull type of anode inaccordance with this invention;

Fig. 5 is a plan View of the anode shown in Fig. 4;

Fig. 6 is a sectional view, taken along the line 6-6 of Fig. 5, and

Fig. 7 is an .isometric view ofa different type of anode in accordancewith this invention, of cylindrical form with a hollow core.

As shown in Fig. 1, a magnesium galvanic anode 10 is continuously formedin a hollow thin wall casting mold 12 of heat-conducting metal which isopen at the top 14 and bottom 16 and attached to a flange 18' restingupon suitable supporting means 20. Surrounding the mold 12 near theupper end thereof is a cooling fluid distributor 22 which is illustratedas a pipe which has apertures or openings 24 directed towards theexterior of the mold wall 32. The cooling fluid is directed through theopenlngs 24 upon the mold wall 32 and thence down the surface of theanode 10, rapidly solidifying and cooling the casting. Molten metal,usually magnesium or aluminum, or alloys thereof, is continuouslyintroduced at a carefully controlled rate into the mold 12 from a sourceof molten metal (not shown) through two pipes 26, 28, which are disposedadjacent to a core rod or strap 30 being fed centrally into the anode 18as it forms. The ends of the pipes 26, 28 which are adjacent to the corerod or strap 30 are so disposed that the molten metal being introducedto the mold 12 impinges on the surface of the rod or core 30. (For adescription of suitable means of controlling the rate of flow of moltenmetal into the mold, see U.S. Patent No. 2,548,696 to Barstow et al.)

The solidified anode 10 is guided and withdrawn by the pinch rolls 34 asthe anode 10 forms and descends below the mold 12. The rate ofintroducing molten metal to the mold 12 is adjusted to maintain abalance with the speed of rotation of the pinch rolls and also inaccordance with the rate of solidification of the metal.

The core rod or strap 30 is guided or fed by the rolls 36 or othersuitable guiding means disposed above the mold 12. The core rod or strap36 should preferably have enough flexibility that it may be uncoiledfrom a spool as needed. Alternatively, the core 30 may be composed of"straight sections which can be welded or otherwise suitably securedtogether to form a continuous core.

The casting operation is as follows: Initially a dummy block, not shown,is inserted against or into the bottom 16 of the mold 12. The dummyblock may have a recess therein for locating the core 30. The core 30 isinserted in the recess and the rolls 36 or other guiding means arepositioned so that the core 30 is perpendicular to the top of the mold12 (or parallel with the sides thereof). Then with the cooling fluid,which may be water, applied against the mold 12, molten metal isintroduced thereto. The metal, when solidified around the bottom part 16and wall 32 of the mold 12, forms a shell which actually becomes themold for the casting. It should be noted that the center portion of thecasting, as might be expected, remains molten for a considerable timeafter the wall portion of the casting has solidified. The solidifiedcasting is then slowly withdrawn downwardly out of the mold 12, normallyat the rate of a few inches per minute, by pinch rolls 34. Since thecore 30 is initially adjusted to be parallel with the side of thecasting or anode 10, it remains so unless the guide rolls 36 becomeimproperly aligned. As is usual in direct chill casting procedure formagnesium, the surface of the melt and the mold 12 may be protected bydirecting sulphur dioxide gas thereon.

When a length of core 30 is almost consumed in making the casting, a newlength is passed through the guide rolls 36 and then is welded orotherwise electrically conductively secured to the free end of the core30 which extends from the anode in such a manner as to maintainalignment of the length of the core 30. Since the anode is being formedat a slow rate, as previously mentioned, the welding together of thecore lengths may be readily accomplished without stopping the continuouscasting of the anode 10. Obviously, core sections may be joined togetherabove the guide rolls 36 as well as below. In some cases, this may bepreferable.

In the embodiment shown in Fig. 1, the molten metal supply pipes 26, 28are so disposed in the melt that the molten metal sweeps against thecore rod or strap 30, and tends to wash or clean the surface thereof.The sweeping of the molten metal against the anode apparently tends toremove any oxide or other surface film which may have collected on thecore 30. This cleaning, and the fact that the core is thoroughlypreheated by passing through the molten metal before the metalsolidifies around the core, apparently greatly enhance the metallurgicalbond between the core 30 and the consumable portion 38 of the anode 10.Also, because the anode is direct chill cast, the anodes may be made inany length required or may be shipped in long lengths which are then cutto smaller anode lengths to fit the needs of the customer buying theanode.

Alternative means of feeding molten metal into the mold 12 areillustrated in Figs. 2 and 3. In Fig. 2, the molten metal is supplied tothe mold 12 through a single pipe 40, the metal being discharged fromthe pipe, as in the arrangement shown in Fig. 1, just under the surface42 of the melt in order to avoid exposure to air of a flowing stream ofmolten metal and to reduce turbulence in the mold. The metal feedingarrangement of Fig. 2 has an advantage in casting anodes with variouscore sizes and shapes, since no close spacing to the core 30 is requiredas in the arrangement shown in Fig. 1.

In the arrangement shown in Fig. 3, the metal is applied through a pipe43 disposed above the surface 42 of molten metal and allowed to flowdown the core 30. This increases the preheating and cleaning of the core30 and tends to cause a constant flow of metal past the surface of thecore 30 as it enters the molten metal in the mold 12.

Anodes made by continuous direct chill castings may be identified eitherby physical appearance or by metallurgical structure. For example, ananode made by continuous direct chill casting is characterized by thelack of shrinkage depressions on the surfaces thereof and by longcolumnar crystal grains transverse to the core of the anode and disposedradially about it. About percent of the total mass, however, may beequiaxed grains, with 10 to 20 percent being columnar grains in asurface layer.

On the other hand, an anode made by the non-continuous permanent moldcasting process heretofore used is characterized by shrinkagedepressions on at least one surface thereof and by the fact thatcolumnar crystal grains extend towards the central axis not only fromthe sides, but also from the ends of the anode.

It should be emphasized that the term magnesium, as applied to materialsfor anodes in this specification, also includes alloys of magnesium.

In Figs. 4, 5, and 6, there is shown an anode 10a made from a shortlength of anode which was made by direct chill casting according to theinvention. The anode 10a is cut as a section of a continuous piece orblank cast according to the process of Fig. l in roughly rectangularcross-section, having a sharp-cornered flat face 44 on one side androunded corners at the other side. The core 30a, in the form of a fiatsteel strap, is cast axially in the anode near the center with its flattransverse face parallel with the flat face 44 of the anode. Holes 46for mounting the anode on stud bolts are drilled in the fiat face 44normal thereto and projecting through the strap 30a, being ofsubstantially smaller diameter than the width of the strap. Enlargedcounterbores 48 are drilled into the anode from the opposite facecoaxial with the holes 46 and extending to the strap 30a. These boresserve to admit the washers and nuts required for holding the anode onmounting studs. The core strap 30a is sufficiently thick to permit theapertures 48 to be drilled deep enough to leave a clean surface of strapmetal exposed without unduly weakening the strap at that point. The corestrap 30a is often galvanized or aluminized, but the use of a coatedcore strap is not essential to the formation of a good bond between thecore 30a and the consumable portion of the anode 10a.

It can be appreciated that galvanic anode blanks made in accordance withthis invention may be readily and economically converted into anodes ofany required length which are capable of being mounted on studs of anydesired mounting center distance. Because of the metallurgical bondbetween the core and the consumable portion of the anode, goodelectrical contact is assured therebetween. This same metallurgical bondalso protects the anode from seepage of fluid between the core and theconsumable portion of the anode. Such seepage may result in theconsuming of the anode portion which is adjacent to the core, finallydestroying electrical contact between the two parts of the anode.

Fig. 7 illustrates a cylindrical anode 10b having a pipe core 30b inaccordance with this invention. This type of anode may be cast in longlengths and then sliced up into disc-like anodes which may beconveniently mounted, as by a bolt through the pipe core 30b. Thecylindrical anode 10b, however, may also be mounted, if desired, insomewhat the same manner as the anode 10a shown in Figs. 4, 5, and 6 bydrilling holes through the anode and core transversely to the axis ofthe core.

The uniformity of spacing of the core 30a within the anodes 10a of thisinvention contributes substantially to their utility, since the drillingmeans may be set to a predetermined depth and then the drilling of theapertures 46 and 48 may be accomplished on automatic drill presses, ifdesired. In anodes made according to prior art practices, it has beendifiicult to accurately position the core 30 within the anode 10 in aneconomical manner.

The excellent metallurgical bond between the core 30 and the consumableportion of the anode assures that a continuously good electrical contactwill be made therebetween for the life of the consumable portion of theanode. This is of considerable importance, since some anodes aredesigned to provide cathodic protection over a period of years tosurfaces which cannot easily be visually inspected, yet if goodelectrical contact between the core and the consumable portion of theanode were broken, little or no cathodic protection Would be provided.

Thus, anodes in accordance with this invention are economical tomanufacture, may be adapted to use in a variety of manners, and arereliable in performance.

This application is a division of copending application, Serial No.430,921, filed May 19, 1954, now abandoned.

I claim:

1. A block like unitary galvanic anode having at least one flat surface,a straight straplike metal core extending through said anode parallelwith said flat surface, at least one aperture extending from said flatsurface through said core, said aperture being smaller than the width ofsaid core, and at least a second aperture of larger diameter than saidfirst mentioned aperture, said second aperture being concentric withsaid first aperture and extend- References Cited in the file of thispatent UNITED STATES PATENTS 2,067,839 Godfrey Jan. 12, 1937 2,092,284McCarroll et a1. Sept. 7, 1937 2,097,508 Blouch Nov. 2, 1937 2,473,478Grebe Aug. 9, 1949 2,486,936 Fergus Nov. 1, 1949 2,763,907 Douglas Sept.25, 1956 2,779,729 Jorgensen Jan. 29, 1957

1. A BLOCK LIKE UNITARY GALVANIC ANODE HAVING AT LEAST ONE FLAT SURFACE,A STRAIGHT STRAPLIKE METAL CORE EXTENDING THROUGH SAID NODE PARALLELWITH SAID FLAT SURFACE, AT LEAST ONE APERTURE EXTENDING FROM SAID FLATSURFACE THROUGH SAID CORE, SAID APERTURE BNEING SMALLER THAN THE WIDTHOF SAID CORE, AND AT LEAST A SECOND APERTURE OF LARGER DIAMETER THANSAID FIRST MENTIONED APERTURE, SAID SECOND APERTURE BEING CONCENTRICWITH SAID FIRST APERTURE AND EXTENDING FROM A SURFACE OF SAID ANODEOTHER THAN SAID FLAT SURFIF-01 FACE TO SAID TCORE MEMBER, SAID FIRST ANDSECOND APERTURES PROVIDING A PASSAGEWAY WHICH EXTENDS BETWEEN OPPOSITELYDISPOSED SURFACES OF THE ANODE.